Trichomonas vaginalis, the causative agent of human trichomoniasis and Tritrichomonas fetus, a parasite of the cattle are aerotolerant anaerobes. The enzymology and subcellular organization of their energy metabolism is further studied. Special attention is paid to the biochemistry of hydrogenosomes, characteristic organelles of anaerobic and aerobic pyruvate oxidation and hydrogen formation. The unique electron transport system of these organelles, especially the iron-sulfur proteins akin to ferredoxin, and the enzymes of their oxidation and reduction will be explored. The interaction of hydrogenosomal enzyme systems with antitrichomonad drugs, also will be studied further, with special attention to possible differences between drug resistant and susceptible strains. The biochemical nature of the hydrolase containing organelles of trichomonads is also explored. These studies will contribute to our understanding of the biology, pathogenic properties and chemotherapeutic responsiveness of T. vaginalis and other trichomonads.